Update Slimmer

Updating Slimmer to 5.0.0 gives us the Report a Problem link at the
bottom of the page.
Use default prechecked state on page load

Rather than always prechecking select boxes, use the prechecked state
from the metadata about an email signup currently pulled from finder-api.
Remove text-align:center from #wrapper

With that declaration, the text in the report a problem link was centre
aligned. This commit removes it to make the text left aligned.
Merge pull request #131 from alphagov/report-a-problem

Report a problem
Merge pull request #130 from alphagov/feature/uncheck-email-signups-by-default-unless-msa

Use default prechecked state on page load